Most jet aircraft are equipped with air conditioning systems, in addition to other environmental control apparatus, to ensure passenger and flight crew comfort and safety. During flight, such air conditioning systems pose no substantial operational problems. The main power plant for the craft will typically provide adequate electric power for the system and will further provide a sufficient source of bleed air for use in ensuring an adequate air flow through the air conditioning system.
Where ground support does not include the provision of electric power, as will often be the case with noncommercial aircraft, some source on the craft itself must be utilized to provide electric power when on the ground. For instance, the main power plant for the craft can be utilized to provide such electric power and bleed air. Operation of the jet engines for such a limited purpose, of course, comprises a most inefficient way of providing such power.
Alternatively, an on-board auxiliary power unit can be provided as a source of electric power. Such auxiliary power units have been wholly inappropriate to date for use on small aircraft of the small cabin class that are rated for no more than sixteen passengers, including both turbo prop and small turbo jet craft, because of their weight. The lightest auxiliary power unit suitable for installation on an aircraft or other small vehicle known to the applicants weighs between 250 and 325 pounds, installed. This weight makes the unit unacceptable by aircraft owners as it reduces the passenger and cargo carrying capacity of small cabin class aircraft to non-useful levels.
There therefore exists a need for a lightweight auxiliary power and forced air supply unit that will weigh less than 200 pounds, installed. Such a unit should provide for a relatively economical source of electricity and a relatively economical source of bleed air and forced air for appropriate use by an on-board air conditioning system. Such a unit should be relative simple to install on existing aircraft, and must be safe for use in aircraft. Beyond this, such a unit should be easily monitored and controlled by the flight crew and include various safety features appropriate to its location and interaction with other aircraft systems.